1. Field of the Invention
The present invention relates to agricultural air seeders, and, more particularly, metering systems used in air carts for metering granular material to be applied to a field.
2. Description of the Related Art
Air seeders are commonly towed by a traction unit, e.g., an agricultural tractor, to apply a product or material such as seed, fertilizer and/or herbicide to a field. An air seeder has as a primary component a wheeled air cart which includes one or more frame-mounted tanks for holding material. In the case of multiple tanks, the tanks can be separate tanks, or a single tank with internal compartments. The air cart is typically towed in combination with a tilling implement, such as an air drill, one behind the other, to place the seed and fertilizer under the surface of the soil. Air seeders generally include a metering system for dispensing material from the tanks and a pneumatic distribution system for delivering the material from the tanks to the soil. A centrifugal fan provides at least one airstream which flows through the pneumatic distribution system. Material is first introduced to the air stream by the metering system at a primary distribution manifold located below the metering system. The tanks are formed with bottom surfaces that slope downward at an angle of repose for the granular material toward the metering system. Gravity, in combination with the vibrations and movement of the air cart, act to move the granular material from the perimeter of the tank toward the metering system located at the center of the tank. Material is carried by the air stream through distribution lines to a series of secondary distribution manifolds, which in turn distribute the material through distribution lines to seed boots mounted behind ground openers on the tilling implement so that the product may be evenly delivered to the ground which is tilled by the tilling implement.
Metering systems are known for their accuracy on level ground, but become inaccurate when operating over hilly terrain. Metering systems can generally handle an elevation change along the metering length (angle change to the meter axis) but become inaccurate front to back (90° to the meter axis). For example, it is known that a 15° slope on hilly terrain can cause a variation in the output rate of product from the metering system of +/−8%. This inaccuracy is due to the change of the bottom meter plate relative to the exit point of the product below the meter roller. The same type of inaccuracy also occurs with metering systems that utilize an auger rather than a roller.
What is needed in the art is an air cart which maintains an accurate output rate of product from the metering system, regardless of the slope of hilly terrain over which the air cart may be operating.